1. Field of the Invention
The present invention relates to a mounting structure of a semiconductor device which can be easily detached from a wiring substrate after being mounted on the wiring substrate and a mounting method thereof.
2. Description of the Related Art
Conventionally, a method is known where a semiconductor chip is mounted on a wiring substrate through solder balls densely provided on one surface of the semiconductor chip. In such a conventional mounting structure of a semiconductor device, resin referred to as underfill is filled into the gap between the semiconductor chip and the wiring substrate. For example, Japanese Patent Application Laid-open No. Hei 10-284635 discloses a semiconductor device in which filling resin is embedded in a gap between a semiconductor chip and a substrate so as to cover solder balls.
With reference to FIG. 7, in such a conventional semiconductor device, a semiconductor chip 21 and a wiring substrate 25 are connected to each other by welded solder balls 26 of the semiconductor chip 21. Further, resin 29 is injected into the gap between the semiconductor chip 21 and the wiring substrate 25 so as to cover the solder balls 26. The resin 29 is injected for the purpose of alleviating the thermal stress caused by the difference in the coefficient of thermal expansion between the semiconductor chip 21 and the wiring substrate 25. The semiconductor chip 21 and the wiring substrate 25 repeat expansion and contraction by heat generated by operations (on/off operation) of the device. However, the coefficient of thermal expansion of the semiconductor chip 21 is about 3.5 ppm whereas the coefficient of thermal expansion of the wiring substrate 25 is about 16 ppm in case of a printed board and about 8 ppm in case of an alumina substrate. Due to this difference in the coefficient of thermal expansion between the semiconductor chip 21 and the wiring substrate 25, the solder balls 26 are alternately subject to compressive stress and tensile stress. As a result, the solder balls 26 are broken at an early stage due to thermal fatigue, which causes electric disconnection, resulting in a signal transmission stop or a power supply stop.
Therefore, by filling the resin 29 into the gap between the semiconductor chip 21 and the wiring substrate 25 so as to cover the solder balls 26. The resin 29 alleviates stress on the solder balls 26. This suppresses the deterioration of the solder balls 26, and the reliability of the connection between the semiconductor chip 21 and the wiring substrate 25 is improved. It is to be noted that epoxy-based resin is mainly used as the resin 29.
However, in the conventional semiconductor device described above, since the semiconductor chip 21 and the wiring substrate 25 are mechanically firmly bonded to each other with the resin 29, once the semiconductor chip 21 is attached to the wiring substrate 25, the semiconductor chip 21 can not be easily detached from the wiring substrate 25. Therefore, there has been a problem in that the semiconductor chip 21 can not be easily replaced and the maintainability is lowered.
An object of the present invention is to provide a mounting structure of a semiconductor device in which a semiconductor chip can be detached from a wiring substrate and high reliability is realized.
According to the present invention, a mounting structure of a semiconductor device with excellent connection reliability can alleviate the stress on solder balls caused by the difference in the coefficient of thermal expansion between a semiconductor chip and a wiring substrate when the semiconductor chip is mounted on the wiring substrate.
Further, according to the present invention, a mounting structure of a semiconductor device with excellent maintainability can be provided in which a semiconductor chip can be easily detached from a wiring substrate after the semiconductor chip has been mounted on the wiring substrate.
According to an aspect of the present invention, in a mounting structure of a semiconductor device, an insulating sheet having a plurality of leads is attached between a semiconductor chip and a wiring substrate, the plurality of leads electrically connecting a plurality of solder balls and a plurality of corresponding connection pads, respectively.
The insulating sheet has holes therethrough at positions corresponding to those of the plurality of connection pads.
One end of each of the plurality of leads is fixed on a first surface of the insulating sheet, while the other end is inserted in one of the holes.
Each of the plurality of solder balls is electrically connected to the fixed one end of a corresponding one of the plurality of leads, while each of the plurality of connection pads is electrically connected to the other end of a corresponding one of the plurality of leads protruding from one of the holes.
According to another aspect of the present invention, a mounting method of a semiconductor device includes providing an insulating sheet having holes therethrough at positions corresponding to those of a plurality of connection pads and having a plurality of leads, one end of each of the plurality of leads being fixed on a first surface of the insulating sheet and the other end of each of the plurality of leads protruding from a second surface of the insulating sheet through one of the holes, electrically connecting the other end of each of the plurality of leads of the insulating sheet to a corresponding one of the plurality of connection pads of a wiring substrate, and electrically connecting each of a plurality of solder balls of a semiconductor chip to the fixed one end of a corresponding one of the plurality of leads.
According to still another aspect of the present invention, an insulating sheet has a plurality of holes therethrough and a plurality of leads, one end thereof being fixed on a first surface of the insulating sheet and the other end thereof being shaped to be afloat in the holes.
According to yet another aspect of the present invention, a method of manufacturing an insulating sheet comprises the steps of providing a metal film on one surface of the insulating sheet, masking and etching the metal film to form a plurality of leads, cutting out predetermined places of the insulating sheet to provide a plurality of holes through the insulating sheet, and making one end of each of the plurality of leads fall into a corresponding one of the plurality of holes.